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earth bending

He's an animal. Wherever the fuck he wants.

I thought Roku's dragon and Roku were buried underneath 5000 tonnes of rock?

Hmmm. I don't remember seeing/hearing anything about that, but Idk, might be wrong.

In one of the later episodes he learns all about Sozin from Roku's spirit and Zuko learns that Roku is his ancestor from history texts.

Roku died when he home island's volcano erupted, he managed to mix earth and fire bending to control the lava, and control water and air at the same time to make sure he didn't breathe toxic fumes and bring in water to cool the eruption.
Roku died when Sozin appeared to "help" and he lost concentration breathing in toxic fumes from the volcano and Sozin let him die, as Sozin lay dying his dragon came over and covered his body with it's own and the last we saw was the lava cascading over them both.

It was one of the final 4 episodes while Aang is on the giant turtle and then talks to Roku. Roku gives an awesome flashback of him and Sozin's relationship, and then it proceeds to show his death when the volcano on his island erupted and Sozin betrayed him.

i dont remember the specifics but aang discovered a seperate group of sky bison i believe around the eastern air temple, although i dont recall where they found them exactly.

That's Ugi, not Appa.

If they did I wonder who made the hole for Appa.

earth bending?

Probably not....But who knows.

Momo is supposed to be the reincarnation of Gyatso